Wheel Imbalance Rejection Module

ABSTRACT

A control system and method for a hydraulic-power steering system of a vehicle including magnetic torque overlay (MTO) is provided. The control system and method minimize undesirable vibration in a hand wheel of the vehicle as a result of disturbance in its front road wheels (e.g., road-wheel imbalance). In the control system and method, a desired torque command is determined or generated. At least the desired torque command is passed to a disturbance-rejection module. The disturbance-rejection module modifies the desired torque command to minimize the vibration.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application claims benefit of the filing date of U.S. Provisional Patent Application 62/030,881 filed on Jul. 30, 2014 and entitled “Wheel Imbalance Rejection Module,” which is incorporated herein by reference in its entirety.

FIELD OF INVENTION

The following description relates to, in general, a magnetic torque overlay (MTO) power steering system of a vehicle and, in particular, functionality of such a system for rejecting undesirable vibrations in the hand wheel of the vehicle due to disturbance in its front road wheels (e.g., road-wheel imbalance).

BACKGROUND

A vehicle is subject to some degree of disturbance in its front road wheels (e.g., road-wheel imbalance). This disturbance can cause undesirable vibrations in the steering wheel or hand wheel detectable by a driver. These vibrations are directly related to the rotational mean velocity of the road wheels. The severity of the vibrations at the hand wheel depends upon both the magnitude of the disturbance and the chassis and steering design.

Methods have been employed to reduce hand wheel vibrations due to road-wheel disturbance. One method is to reduce the source of the disturbance. However, this approach has practical limitations. For example, in the case of road-wheel imbalance, there are changes in the imbalance over tire and wheel wear.

Another method is to minimize transmissibility of the disturbance to the driver. The transmissibility is affected by physical design of the chassis and steering system and tuning of the steering system. However, there are limitations to such minimization because of trade-offs with other design considerations.

In vehicles equipped with electric-power steering (EPS), another method is to minimize transmissibility of road-wheel imbalance—namely, targeted algorithms are specifically aimed at rejecting disturbance due to road-wheel imbalance. With such an approach, it is possible to reject the disturbance with minimal impact on other aspects of performance of the system. In vehicles equipped with hydraulic-power steering (HPS), the transmissibility has been minimized through mechanical methods, such as selection of torsional stiffness of T-bars, increased friction, and mounting stiffness.

SUMMARY OF INVENTION

A system and method to minimize or eliminate undesirable vibration in a hand wheel of a vehicle as a result of disturbance in its front road wheels (e.g., road-wheel imbalance) in a hydraulic-power steering system (HPS system) including magnetic torque overlay (MTO) is provided.

In one non-limiting exemplary embodiment of the invention, a control system and method for the MTO steering system is provided. In the system and method, a desired torque command is determined or generated. At least the desired torque command is passed to a disturbance-rejection module. The disturbance-rejection module modifies the desired torque command to minimize vibration at the hand wheel. A resulting final torque command is provided to a current-command module that converts the desired torque command into a required current command. The required current command is applied to a coil of a magnetic actuator in a steering gear of the MTO steering system. At least the required current command is used to generate an estimation of torque by a driver of the vehicle.

In an aspect of this embodiment, a measurement of differential pressure across a piston in the MTO steering system and various signals of the vehicle and an estimation of torque signals of the driver are used to generate the desired torque command. In a version of this aspect, the vehicle signals include speed of the vehicle (i.e., front wheels) and angle of the hand wheel. In another aspect, the driver-torque-signal estimation, hand-wheel angle, and vehicle speed are passed also to the disturbance-rejection module. In still another aspect, the measured differential pressure is used also to generate the driver-torque estimation.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter that is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawing in which:

FIG. 1 is a schematic diagram illustrating a non-limiting exemplary embodiment of a vehicle including a hydraulic-power steering system (HPS system);

FIG. 2 is a dataflow diagram illustrating a non-limiting exemplary embodiment of a control module in accordance with the HPS system of FIG. 1;

FIG. 3 is a block diagram illustrating a control system for a power steering system including magnetic torque overlay (MTO);

FIG. 4 is a block diagram illustrating a non-limiting exemplary embodiment of a control system including disturbance rejection in accordance with the invention for the MTO steering system;

FIG. 5 is a block diagram illustrating a non-limiting exemplary embodiment of a disturbance-rejection module in accordance with the control system of FIG. 4;

FIG. 6 is a block diagram illustrating implementation of a non-limiting exemplary embodiment of a notch filter in accordance with the disturbance-rejection module of FIG. 5;

FIG. 7 is a block diagram illustrating implementation of a non-limiting exemplary embodiment of a notch-filter gain in accordance with the notch filter of FIG. 6;

FIG. 8 is a block diagram illustrating implementation of a non-limiting exemplary embodiment of a disturbance-rejection subsystem in accordance with the disturbance-rejection module of FIG. 5;

FIG. 9 is a block diagram illustrating implementation of a non-limiting exemplary embodiment of adaptive filters in accordance with the disturbance-rejection subsystem of FIG. 8;

FIG. 10 is a block diagram illustrating implementation of a non-limiting exemplary embodiment of a phase-adjust subsystem in accordance with the disturbance-rejection subsystem of FIG. 8;

FIG. 11 is a block diagram illustrating another non-limiting exemplary embodiment of the disturbance-rejection module including disturbance rejection in accordance with the invention for the MTO steering system;

FIG. 12 is a block diagram illustrating implementation of a non-limiting exemplary embodiment of a hand-wheel-motion-reduction subsystem in accordance with the disturbance-rejection module of FIG. 11;

FIG. 13 is a block diagram illustrating implementation of a non-limiting exemplary embodiment of a gain-and-pole-magnitude subsystem in accordance with the hand-wheel-motion-reduction subsystem of FIG. 12; and

FIG. 14 is a flowchart illustrating a non-limiting exemplary embodiment of a control method in accordance with the invention for the MTO steering system.

DETAILED DESCRIPTION

Throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. Referring now to the Figures, the invention will be described with reference to specific exemplary embodiments thereof without limiting same. FIG. 1 is a schematic diagram illustrating a non-limiting exemplary embodiment of a vehicle 10 including a hydraulic-power steering system (HPS system) 12.

As shown in the FIG. 1, the steering system 12 includes a steering wheel or hand wheel 14 coupled to a steering shaft 16 of the vehicle 10 and a steering-assist unit 18 that couples to the steering shaft 16 and tie rods 20, 22 of the vehicle 10. During operation, as the hand wheel 14 is turned by a driver of the vehicle 10, the steering-assist unit 18 provides assistance to move the tie rods 20, 22, which, in turn, move corresponding steering knuckles 24, 26 coupled to front road wheels 28, 30 of the vehicle 10.

The vehicle 10 includes further various sensors 32, 34, 36 that detect and measure observable conditions of the steering system 12 and/or vehicle 10. The sensors 32, 34, 36 generate sensor signals based upon the observable conditions. The sensors 32, 34, 36 can include, for example, a load sensor, driver-torque sensor, and/or position sensor. A control module 38 controls operation of the steering system 12 and/or vehicle 10 based upon one or more of the sensor signals and control system and method of the present disclosure. Generally speaking, dynamic response of the steering system 12 is measured or calculated, and command signals to the steering system 12 are modified such that desired results are achieved. A disturbance-cancel command is modified in such a way that, when applied to a torque signal, the vehicle 10 is controlled in a desired manner to counteract a disturbance into the steering system 12 (in particular, the road wheels 28, 30). Road-wheel imbalance is an example of a type of such disturbance.

It is desired to achieve a result with regard to the steering-assist unit 18—for example, by rejecting the disturbance. It should be readily appreciated that, while not shown here, the system and method can also be made variable based upon other features and/or variables of the steering system 12. Some examples include torque of the hand wheel 14 and speed of the vehicle 10.

FIG. 2 is a dataflow diagram illustrating a non-limiting exemplary embodiment of a control module 38 used to control the steering system 12. The control module 38 can include at least one sub-module and datastore. As used herein, the terms “module” and “sub-module” refer to an application-specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group), and memory that executes at least one software or firmware program, a combinational logic circuit, and/or other suitable components that provide described functionality. It should be readily appreciated that the sub-modules can be combined and/or further partitioned to reduce steering-torque variation and implemented as a single control module 38 (as shown) or multiple control modules (not shown). Inputs to the control module 38 can be generated from the sensors 32, 34, 36, modeled within the control module 38 [e.g., by other sub-modules (not shown)], received from other control modules (not shown), and/or pre-defined.

As shown in FIG. 2, the control module 38 includes a power-steering module 40. The power-steering module 40 performs control methods—such as, but not limited to, assist methods and damping methods. Depending upon the control methods, output can be a control signal 42 requesting a torque.

An HPS system including Magnetic Steer (Magnasteer) Torque Overlay (MTO) 12 incorporates a magnetic actuator in a hydraulic-valve assembly. This allows advanced features to be implemented on the MTO steering system 12, such as variable effort, leads-and-pulls correction, active damping, and active return. In many cases, tuning of these advanced features desired for optimal feel of steering of the vehicle 10 increases transmissibility of the disturbance into the MTO steering system 12—in particular, in the road wheels 28, 30.

The disturbance can cause undesirable vibrations in the hand wheel 14 detectable by the driver. These vibrations are directly related to the rotational mean velocity of the road wheels 28, 30. The severity of the vibrations at the hand wheel 14 depends upon both the magnitude of the disturbance and the chassis and steering design.

FIG. 3 is a block diagram illustrating a control system 50 of an MTO steering system. In the control system 50, as shown in FIG. 3, a desired MTO torque command is determined or generated in a torque-command module 52. More specifically, a measurement of differential pressure across a piston (not shown) in the MTO steering system and various signals of the vehicle 10 and an estimation of torque signals of the driver can be used to generate the desired torque command. Toward this end, the vehicle signals can include speed of the vehicle 10 (i.e., road wheels 28, 30) and angle of the hand wheel 14. The desired torque command is provided to a current-command module 54 that converts the desired torque command into a required current command. The required current command is applied to a coil (not shown) of a magnetic actuator (not shown) in a steering gear (not shown) of the MTO steering system. The required current command and measured differential pressure are used to generate in a driver-torque-estimation module 56 an estimation of torque by the driver.

FIGS. 4-13 illustrate a non-limiting exemplary embodiment of a control system 58 for the MTO steering system 12 according to the invention. The control system 58 includes functionality in the form of disturbance rejection for rejecting the undesirable vibrations in the hand wheel 14 due to the disturbance in the road wheels 14 (i.e., road-wheel imbalance). Toward that end, the control module 38 (FIGS. 1 and 2) includes also a disturbance-rejection algorithm or module 60—in particular, wheel-imbalance-rejection module 60 (WIR module 60). The WIR module determines a force of a disturbance acting upon the steering-assist unit 18 (FIG. 1), for example, and generates a frequency signal 62 (such as, but not limited to, a WIR command or hand-wheel-motion command). In FIGS. 4-13, logic implemented in the WIR module 60 is shown.

More specifically, FIG. 4 is a block diagram illustrating the control system 58 including the WIR module 60. In the control system 58, as shown in FIG. 4, a desired MTO torque command is determined or generated in a torque-command module 64. In an aspect of the embodiment, a measurement of differential pressure across the piston in the MTO steering system 12 and various signals of the vehicle 10 and an estimation of torque signals of the driver are used to generate the desired torque command. In a version of this aspect, the vehicle signals include speed of the vehicle 10 (i.e., road wheels 28, 30) and angle of the hand wheel 14. At least the desired torque command is passed to the WIR module 60. In another version, the driver-torque-signal estimation, hand-wheel angle, and vehicle speed can be passed also to the WIR module 60. The WIR module 60 modifies the desired torque command to minimize vibration at the hand wheel 14. A resulting final torque command is provided to a current-command module 66 that converts the desired torque command into a required current command. The required current command is applied to the coil of the magnetic actuator in the steering gear of the MTO steering system 12. At least the required current command is used to generate in a driver-torque-estimation module 68 an estimation of torque by the driver. In still another version, the measured differential pressure is used also to generate the driver-torque estimation.

FIG. 5 is a block diagram illustrating a non-limiting exemplary embodiment of the WIR module 60. As shown in FIG. 5, in right and left wheel-speed-conversion-and-filter modules 70, 72, signals for corresponding individual wheel speeds are scaled and low-pass filtered to provide a signal for filtered frequency, and a signal for unfiltered frequency is scaled to radians per second. Filtered right and left wheel-speed frequencies are averaged to determine a signal for estimated frequency. The torque command is run through a notch filter 74 to remove frequency content of the torque command at the estimated frequency of the wheel speeds. Wheel-speed-frequency signals and a hand-wheel-angle signal are provided to and run through a WIR subsystem 76. In this way, the torque command is produced to aid in reduction or elimination of undesirable vibration at the hand wheel 14 due to wheel imbalance.

FIG. 6 is a block diagram illustrating implementation of a non-limiting exemplary embodiment of the notch filter 74. As shown in FIG. 6, an estimated frequency is used to determine coefficients of a unity-gain-resonance filter 78 with a pole located at a wheel-imbalance frequency for a current operating speed. The torque command is run through the unity-gain-resonance filter 78 to extract content at the wheel-imbalance frequency. The estimated average frequency and estimated torque of the hand wheel 14 run through a notch-filter-gain module 80. The filtered torque command is multiplied by a gain value (e.g., 0 to 1), and the resulting product is subtracted from the original signal to remove filtered-frequency content from a final command. A gain value allows the notch filter 74 to be applied only when conditions require it.

FIG. 7 is a block diagram illustrating implementation of a non-limiting exemplary embodiment of the notch-filter-gain module 80. FIG. 7 shows implementation in which a look-up table based upon a filtered value of estimated driver torque and look-up table based upon estimated frequency are used to enable the notch filter 74 when both driver torque and wheel frequency are in a desired range. Referring again to FIG. 5, the command produced by the WIR subsystem 76 is added to the notch-filtered torque command to produce a final torque command. It should be readily appreciated that any suitable type of signal can be used to change gain.

FIG. 8 is a block diagram illustrating implementation of a non-limiting exemplary embodiment of the WIR subsystem 76. As shown in the figure, unfiltered right and left wheel speeds are passed through individual unity-gain-resonance filters 78. Filtered wheel speeds are used to determine the filter coefficients for the unity-gain-resonance filters 78 with a pole located at a wheel-imbalance frequency for a current operating speed. Output of each filter is passed through a tapped delay to provide a predetermined number of samples as a reference signal to a right or left adaptive filter 82, 84. The hand-wheel-angle signal is first passed through a high-pass filter 86 to remove direct-current content and then used in calculation of coefficients for the individual adaptive filters 82, 84. The adaptive filters 82, 84 provide a command to minimize frequency content of the hand-wheel-angle signal that correlates to the reference signal (i.e., filtered wheel speeds). The adaptive filters 82, 84 can be powered on and off with an enabling signal. The figure shows an enabling signal that is generated by a look-up table based upon estimated wheel frequency.

FIG. 9 is a block diagram illustrating implementation of a non-limiting exemplary embodiment of the adaptive filters 82, 84. The example shown is based upon a least-mean-squares algorithm (LMS algorithm). The LMS algorithm changes filtered-tap weights so that error (eps) is minimized in a mean-square sense. It should be readily appreciated that, although the LMS algorithm is applied here due to its computational efficiency, other iterative search algorithms may be employed. It should be readily appreciated that any suitable type of signal can be used to change gain.

In FIG. 9, PrevEpsilon input is used as an error signal for learning (e.g., hand-wheel angle). It should be readily appreciated that hand-wheel velocity and acceleration are also suitable error signals (as oscillation within the signal is relevant). Reference signal input x Ref (FIG. 8) is filtered wheel speed. Learning is active when enable is non-zero. Enable is commonly “1” when learning is desired. However, it should be readily appreciated that other values for enable may be used if additional frequency scaling is desired. A basic function is to filter x Ref to generate an output. This is accomplished at each time step by multiplying elements of vectors x Ref times a vector that represents filter weights. A number of elements in the vectors is determined by right and left Tapped Delay blocks 88, 90 (FIG. 8). Filter-learning speed is controlled by constant AdaptiveMu multiplied by two. Output of the two adaptive filters 82, 84 are summed together to provide a torque command to reduce vibration of the hand wheel 14 that correlates to measured wheel imbalance. The torque command is passed through a phase-adjust subsystem 92 (FIG. 8) to account for steady-state-system lags between the torque command and physical torque produced. Also, the two unity-gain-resonance filters 78 (FIG. 8) can likewise be brought together and passed through the Tapped Delay block 88 and adaptive filter 82.

FIG. 10 is a block diagram illustrating implementation of a non-limiting exemplary embodiment of the phase-adjust subsystem 92. In this implementation, amount of phase adjust can be varied by a look-up table based upon average wheel frequency. Referring again to FIG. 8, output of the phase-adjust subsystem 92 is limited and scaled to produce final output of the WIR subsystem 76.

FIG. 11 is a block diagram illustrating another non-limiting exemplary embodiment of the disturbance-rejection module 94 including disturbance rejection. As shown in FIG. 11, this embodiment differs in that the WIR subsystem 76 is replaced with a hand-wheel-motion-reduction subsystem 96. Estimated-wheel-speed-frequency signal, estimated-driver-torque signal, and hand-wheel-angle signal are provided to the hand-wheel-motion-reduction subsystem 96 to produce a torque command to aid in reduction or elimination of undesirable vibration at the hand wheel 14 due to wheel imbalance. The torque command produced by the hand-wheel-motion-reduction subsystem 96 is added to the notch-filtered torque command to produce a final torque command.

FIG. 12 is a block diagram illustrating implementation of a non-limiting exemplary embodiment of the hand-wheel-motion-reduction subsystem 96. As shown in FIG. 12, in a gain-and-pole-magnitude subsystem 98, wheel-speed frequency and estimated driver torque are used to determine pole magnitude of the unity-gain-resonance filter 78 and gain of the hand-wheel-motion-reduction subsystem 96.

FIG. 13 is a block diagram illustrating implementation of a non-limiting exemplary embodiment of the gain-and-pole-magnitude subsystem 98. In this implementation, look-up tables based upon driver torque, wheel-speed frequency, and wheel-speed-frequency change are used to modify gain and filtered-pole magnitude.

Referring again to FIG. 12, pole magnitude and wheel-speed frequency are used to calculate filter coefficients for a unity-gain-resonance filter 78 with a pole located at a wheel-imbalance frequency for a current operating speed. A hand-wheel-angle signal is passed through the unity-gain-resonance filter 78 to provide an amount of hand-wheel vibration at the wheel-imbalance frequency. Output of the unity-gain-resonance filter 78 is passed through a phase-adjust subsystem 92. Output of the phase-adjust subsystem 92 is multiplied by gain previously determined in the gain-and-pole-magnitude subsystem 98, and the resulting product is limited to produce final output of the hand-wheel-motion-reduction subsystem 96.

With continued reference to FIGS. 1 and 2, FIG. 14 is a flowchart illustrating a non-limiting exemplary embodiment of a control method 100 for the steering system 12. The method 100 can be performed by the control module 38 of FIG. 1 in accordance with the present disclosure. As can be appreciated in light of the present disclosure, order of operation within the method 100 is not limited to sequential execution as illustrated in FIG. 14, but may be performed in at least one vary order as applicable and in accordance with the present disclosure. The method 100 can be scheduled to run based upon predetermined events and/or run continually during operation of the steering system 12.

The method 100 includes, at step 102, determining or generating in the torque-command module 64 the desired torque command; at step 104, passing at least the desired torque command to the WIR module 60; at step 106, modifying the desired torque command via the WIR module 60; and, at step 108, minimizing vibration at the hand wheel 14. Continuing, the method includes, at step 110, providing the resulting final torque command to the current-command module 66; at step 112, converting the desired torque command into the required current command; and, at step 114, applying the required current command to the coil of the magnetic actuator in the steering gear of the MTO steering system 12. At step 116, at least the required current command is used to generate in the driver-torque-estimation module 68 the estimation of torque by the driver.

In an aspect of this embodiment, the method 100 includes further, at step 118, using the measurement of differential pressure across the piston in the MTO steering system 12 and various signals of the vehicle 10 and the estimation of torque signals of the driver to generate the desired torque command. In a version of this aspect, the method 100 includes further, at step 120, including as the vehicle signals the speed of the vehicle 10 (i.e., road wheels 28, 30) and angle of the hand wheel 14. In another aspect, the method includes, at step 122, passing also the driver-torque-signal estimation, hand-wheel angle, and vehicle speed to the WIR module 60. In still another aspect, the method 100 includes further, at step 124, using the measured differential pressure also to generate the driver-torque estimation.

The system 52 and method 100 minimize or eliminate undesirable vibrations in the hand wheel 14 of the vehicle 10 as a result of disturbance in the road wheels 28, 30 (e.g., road-wheel imbalance) in the MTO steering system 12.

While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description. 

1. A method of reducing vibration in a hand wheel of a steering system of a vehicle including magnetic torque overlay (MTO), the method comprising: determining a desired torque command; passing at least the desired torque command to a disturbance-rejection module; and modifying the desired torque command to minimize the vibration.
 2. The method of claim 1, further comprising: providing a resulting final torque command to a current-command module that converts the desired torque command into a required current command; applying the required current command to a steering gear of the MTO steering system; and using at least the required current command to generate an estimation of torque by a driver of the vehicle.
 3. The method of claim 2, wherein at least one of differential pressure across the MTO steering system and at least one signal of the vehicle is measured and the measurement is used to generate the desired torque command.
 4. The method of claim 3, wherein the differential pressure is across a piston in the MTO steering system.
 5. The method of claim 3, wherein the at least one vehicle signal includes at least one of speed of the vehicle and angle of the hand wheel.
 6. The method of claim 5, wherein the speed of the vehicle includes speed of at least one front road wheel of the vehicle.
 7. The method of claim 5, wherein at least one torque signal of a driver of the vehicle is estimated and the estimate is used to generate the desired torque command.
 8. The method of claim 7, wherein at least one of the driver-torque-signal estimation, hand-wheel angle, and vehicle speed is passed to the disturbance-rejection module.
 9. The method of claim 2, wherein the required current command is applied to a coil of a magnetic actuator in the steering gear.
 10. The method of claim 2, wherein the driver-torque estimation is generated in a driver-torque-estimation module.
 11. The method of claim 3, wherein the measured differential pressure is used to generate the driver-torque estimation.
 12. The method of claim 1, wherein the desired torque command is determined in a torque-command module.
 13. The method of claim 1, wherein the desired torque command is modified via the disturbance-rejection module.
 14. A system for controlling a steering system of a vehicle including magnetic torque overlay (MTO), the control system comprising: a disturbance-rejection module configured to determine a force of disturbance acting upon the steering system and generate a disturbance-rejection command; a torque-command module configured to produce an MTO torque command as a function of at least one of an estimated wheel-speed-frequency signal, an estimated driver-torque signal, and a hand-wheel-angle signal, the torque command being passed to the disturbance-rejection module; and a notch filter through which the torque command is run to produce a final MTO torque command.
 15. The control system of claim 14, wherein the disturbance-rejection module includes at least one wheel-speed-conversion-and-filter module, at least one signal for a corresponding wheel speed is scaled and low-pass filtered to provide a signal for filtered frequency, and a signal for unfiltered frequency is scaled.
 16. The control system of claim 15, wherein filtered wheel-speed frequencies are averaged to determine a signal for estimated frequency and the notch filter removes frequency content of the torque command at the estimated frequency of the wheel speed.
 17. The control system of claim 14, further comprising: a disturbance-rejection subsystem, the wheel-speed-frequency signal and hand-wheel-angle signal being provided to and running through the disturbance-rejection subsystem such that the MTO torque command is produced to aid in reduction of vibration in the steering system.
 18. The control system of claim 17, further comprising: at least one unity-gain-resonance filter through which unfiltered wheel speed is passed, the filtered wheel speed being used to determine a coefficient for the filter with a pole located at a disturbance frequency for a current operating speed; a tapped delay through which output of the filter is passed to provide a predetermined number of samples as a reference signal to an adaptive filter; a high-pass filter through which the hand-wheel-angle signal is passed to remove direct-current content, the hand-wheel-angle signal being used in calculation of the coefficient; and a command provided via the adaptive filter to minimize frequency content of the hand-wheel-angle signal that correlates to the reference signal.
 19. The control system of claim 18, wherein implementation of the adaptive filter is based upon a least-mean-squares algorithm that changes filtered-tap weights so that error is minimized in a mean-square sense.
 20. The control system of claim 14, wherein the torque command is passed through a phase-adjust subsystem configured to account for steady-state-system lags between the torque command and physical torque produced. 